signal: In get_signal test for signal_group_exit every time through the loop

Recently while investigating a problem with rr and signals I noticed
that siglock is dropped in ptrace_signal and get_signal does not jump
to relock.

Looking farther to see if the problem is anywhere else I see that
do_signal_stop also returns if signal_group_exit is true.  I believe
that test can now never be true, but it is a bit hard to trace
through and be certain.

Testing signal_group_exit is not expensive, so move the test for
signal_group_exit into the for loop inside of get_signal to ensure
the test is never skipped improperly.

This has been a potential problem since I added the test for
signal_group_exit was added.

Fixes: 35634ffa1751 ("signal: Always notice exiting tasks")
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/875yssekcd.fsf_-_@email.froward.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/kernel/signal.c b/kernel/signal.c
index 7c4b7ae..986fa69 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2662,19 +2662,19 @@ relock:
                goto relock;
        }
 
-       /* Has this task already been marked for death? */
-       if (signal_group_exit(signal)) {
-               ksig->info.si_signo = signr = SIGKILL;
-               sigdelset(&current->pending.signal, SIGKILL);
-               trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
-                               &sighand->action[SIGKILL - 1]);
-               recalc_sigpending();
-               goto fatal;
-       }
-
        for (;;) {
                struct k_sigaction *ka;
 
+               /* Has this task already been marked for death? */
+               if (signal_group_exit(signal)) {
+                       ksig->info.si_signo = signr = SIGKILL;
+                       sigdelset(&current->pending.signal, SIGKILL);
+                       trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
+                               &sighand->action[SIGKILL - 1]);
+                       recalc_sigpending();
+                       goto fatal;
+               }
+
                if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) &&
                    do_signal_stop(0))
                        goto relock;